The source line debug info generation assumed that the function would
have debug info. Check for a non-null di_subprogram_ to ensure we are
emitting debug info for the function.
Rather than checking the di_builder_ - this way if we implement
`nodebug` function attributes, it'll fall out naturally (by creating a
null di_subprogram_) rather than having to come back and change this
from "is debug info enabled" to "is debug info enabled for this
function" later on.
Discussed in the toolchain meeting today - we'd like to try having this
on by default and see if the cost isn't too high.
The nodebug test is a bit verbose, because it doesn't have the
`--exclude-dump-file-prefix` that test_file would usually add. Is there
a nicer way I could write this test to verify that --no-debug-info does
what it's meant to?
David Blaikie